Modelling Thermal Conductivity of Porous Thermal Barrier Coatings

Ghai, Ramandeep Singh; Chen, Kuiying; Baddour, Natalie

doi:10.3390/coatings9020101

Cited by 17 publications

(10 citation statements)

References 82 publications

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“…The granular form of the voids can be explained by the partial melting of large agglomerated particle clusters in the plasma jet during the APS process. The pores and their granular structure serve to reduce the thermal conductivity of the coating due to the strong phonon scattering from the air entrapped in the pores and/or boundaries of unmelted particles [36,[41][42][43][44]. Figure 4 shows the EDX spectrum for particles and granules that described above with peaks for the YAG top coat constituent elements Y, Al and O.…”

Section: X-ray Diffractionmentioning

confidence: 99%

Thermal shock resistance of yttrium aluminium oxide Y3Al5O12 thermal barrier coating for titanium alloy

Almomani¹,

Al‐Widyan²,

Mohaidat³

2020

JMES

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The high strength-to- weight ratio of titanium alloys allows their use in jet engines. However, their use is restricted by susceptibility to oxidation at high temperatures. In this study, the possibility of increasing the operating temperature of titanium alloys through using Yttrium Aluminum Oxide (YAG) as a thermal barrier coating material for Ti-6Al-4V substrate is studied. The study concludes that YAG can be utilized to increase the operating temperature of Ti-6Al-4V titanium alloy from around 350 °C to 800 °C due to its low thermal conductivity and phase stability up to its melting point. In addition, its lower oxygen diffusivity in comparison with the standard YSZ material will provide a better protection of the titanium substrate from oxidation. In this work, coating was created using atmospheric plasma spray. X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) were used to examine coatings' composition and structure. The coating was characterized by thermal shock test, Vickers hardness test and adhesion strength test. X-ray diffraction indicated that the coating was of a partially crystalline Y3Al5O12 composition. The coating was porous with excellent thermal shock resistance at 800 oC, with a Vickers micro-hardness of 331.35 HV and adhesion strength of 17.6 MPa.

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Section: X-ray Diffractionmentioning

confidence: 99%

Thermal shock resistance of yttrium aluminium oxide Y3Al5O12 thermal barrier coating for titanium alloy

Almomani¹,

Al‐Widyan²,

Mohaidat³

2020

JMES

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“…Cernuschi et al extended the Bruggeman model to a four‐phase system by the iterative approach to describe three different kinds of defects and the predicted thermal conductivity agreed well with the measured values 9 . Ghai et al developed a five‐phase model using a similar approach 44 . In addition to analytic models, various numerical studies have also been developed to deal with defects.…”

Section: Introductionmentioning

confidence: 97%

Thermal conductivity prediction in air plasma sprayed thermal barrier coatings containing multifarious defects

Zhao

Ren

et al. 2021

J Am Ceram Soc

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Air plasma sprayed yttria‐stabilized zirconia thermal barrier coatings are widely applied in gas turbines and aviation engines, which usually contain multifarious and multiscale defects, such as pores, cracks, and amorphous layers. They all significantly lower the thermal conductivity of the coating but in drastically different ways depending on their morphologies and orientations. Establishing an accurate correlation between the microstructure and the thermal conductivity requires not only a precise separation and estimation of different kinds of defects but also a reasonable mathematic model to describe their effect on thermal conductivity. In this research, cross‐section ion polishing and image analysis were chosen as a reliable assembly for characterizing multifarious defects of porous coatings, which was almost undamaged compared with the traditionally mechanical polishing. The effect of different microscale defects on the thermal conductivity was respectively and quantitatively studied to build a mathematical model. A thermal resistance induced by amorphous layers was introduced into the model, which was found to have a linear relationship with the amorphous layer concentration. It was also found a linear relationship between the amorphous layer concentration and the spraying times. The predicted thermal conductivity of porous coatings by multifarious‐defect‐concerned model fits the data measured using the steady heat flow method very well. This research confirms the applicability of image‐analysis‐based modeling as a simple, reliable, and versatile method for thermal conductivity prediction of porous coating systems.

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“…Significant technological advances have led to increasing operating temperatures and pressures in recent decades, enhancing the efficiency of gas turbines to over 40%. These technological advances include coatings, heat treatments, a new superalloy permitting high operating temperatures, and a new cooling system [4][5][6][7][8][9][10][11]. Specifically, an F-class gas turbine, which operates at approximately 1300 • C and a pressure ratio of 16 during full-load conditions, was developed in the late 1990s and deployed to many thermal power plants.…”

Section: Introductionmentioning

confidence: 99%

Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation

Chang

2019

Coatings

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In this study, the contribution of high thermomechanical fatigue to the gas turbine lifetime during a steady-state operation is evaluated for the first time. An evolution of the roughness on the surface between the thermal barrier coating and bond coating is addressed to elucidate the correlation between operating conditions and the degradation of a gas turbine. Specifically, three factors affecting coating failure are characterized, namely isothermal operation, low-cycle fatigue, and high thermomechanical fatigue, using laboratory experiments and actual service-exposed blades in a power plant. The results indicate that, although isothermal heat exposure during a steady-state operation contributes to creep, it does not contribute to failure caused by coating fatigue. Low-cycle fatigue during a transient operation cannot fully describe the evolution of the roughness between the thermal barrier coating and the bond coating of the gas turbine. High thermomechanical fatigue during a steady-state operation plays a critical role in coating failure because the temperature of hot gas pass components fluctuates up to 140 °C at high operating temperatures. Hence, high thermomechanical fatigue must be accounted for to accurately predict the remaining useful lifetime of a gas turbine because the current method of predicting the remaining useful lifetime only accounts for creep during a steady-state operation and for low-cycle fatigue during a transient operation.

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Modelling Thermal Conductivity of Porous Thermal Barrier Coatings

Cited by 17 publications

References 82 publications

Thermal shock resistance of yttrium aluminium oxide Y3Al5O12 thermal barrier coating for titanium alloy

Thermal shock resistance of yttrium aluminium oxide Y3Al5O12 thermal barrier coating for titanium alloy

Thermal conductivity prediction in air plasma sprayed thermal barrier coatings containing multifarious defects

Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation

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